Identification of genes deregulated during serum-free medium adaptation of a Burkitt's lymphoma cell line.

Serum is usually added to growth media when mammalian cells are cultured in vitro to supply the cells with growth factors, hormones, nutrients and trace elements. Defined proteins and metal ions, such as insulin, growth factors, transferrin and sodium selenite, are sometimes also included and can in some cases substitute serum components. How adaptation to serum free media influences cells has not been studied in detail. We have adapted the Burkitt's lymphoma line Ramos to a serum-free medium that supports long-term survival and studied gene expression changes that occurred during the adaptation process. The adaptation process was characterized by initial cell population growth arrest, and after that extensive cell death, followed by proliferation and long-term survival of clonal cultures. Proliferation and cell cycle progression of the serum-free cultures closely mimicked that of serum-dependent cells. Affymetrix micro-array technology was used to identify gene expression alterations that had occurred during the adaptation. Most changes were subtle, but frequently the genes with altered expression were involved in basal cellular functions such as cell division, cell cycle regulation, apoptosis and cell signalling. Some alterations were restored when the cells were transferred back to serum-containing medium, indicating that expression of these genes was controlled by components in serum. Others were not, and may represent changes that were selected during the adaptation process. Among these were, for example, several genes within the Wnt signalling pathway.